The invention relates to a method for preventing a motor vehicle from rolling away, wherein the motor vehicle comprises an automated manual transmission, preferably a dual-clutch transmission, which engages a gear when the selector lever is in a NEUTRAL position.
DE 100 59 276 A1 makes known a method for operating a motor vehicle, in which a vehicle brake must be actuated in order to set a transmission ratio in a transmission. If the selector lever is in the neutral position at this time, a transmission ratio is not set. If the selector lever is moved from the neutral position into a drive position, a check is carried out to determine whether or not the vehicle brake has been actuated. If the vehicle brake has been actuated, a corresponding transmission ratio is set. If the vehicle brake is not actuated, a transmission ratio is not set.
EP 1 155 899 B1 discloses a method for detecting an intention of a driver to start driving in the case of a motor vehicle equipped with a self-shifting transmission. In this case, the electronic control of a self-shifting transmission in the motor vehicle detects, by way of the selector lever being moved from NEUTRAL into a driving gear, that the driver wants to start driving, even if a service brake has not been actuated before the driving gear is selected. In this case, it is still ensured, however, that an inadvertent displacement of the selector lever will not initiate driving.
Automated manual transmission systems that also have a gear engaged in the NEUTRAL selector lever position are known. This gear is coupled via an overrunning clutch to the transmission output and is not actuated by the transmission control unit. This means the transmission control unit has actively engaged NEUTRAL in all sub-transmissions. The transmission input shaft is nevertheless coupled to the transmission output shaft via an overrunning clutch. Next, with the engine running and the clutch disengaged, if a drag torque is transmitted by the clutch to the transmission input shaft, then, depending on the level of the drag torque and the particular transmission ratio of the engaged gear, the motor vehicle is nevertheless accelerated due to the transmission ratio of the engaged gear. In the following, the drag torque should be considered to be a torque that can be transmitted even when the clutch is disengaged, which is the case, in particular, with wet clutches.
Such a movement of the motor vehicle is a safety-critical situation, however, which must be avoided in any event, in particular when the vehicle driver parks the motor vehicle with the selector lever in the NEUTRAL position and leaves the motor vehicle.